stc15f104 realizes touch switch

I want to make a small controller that can be turned on with a touch and turned off with a delay

Using an ordinary touch switch seems ugly, and the switch is not convenient to fix. It is not a good idea to put the control panel outside, right?

I want to use a touch switch, but I haven't found a suitable one after searching online for a long time. There is a capacitive sensing switch in the official STC document.

It needs to occupy 2 IO, one to generate PWM signal and one for AD judgment. In addition, it also needs 2 resistors, 2 diodes and 1 capacitor.

It felt a bit complicated, so I tried it and finally got it done with just one IO port, one resistor and one capacitor.

The idea is this:

A 2M resistor connects the power supply and IO port (I used p3.3)

A 33p capacitor is connected between the IO port and ground.

Connect a wire from the IO port to a metal sheet or something for touch.

Set p3.3 to 0 to discharge the capacitor first, then set it to high impedance state. At this time, the power supply will charge the capacitor through the resistor.

The time constant 2M*33p is about 66μs. The timer is used to count the time when the io port becomes high level.

If you don't use a timer, you may be affected by interruptions and there may be errors.

This time may need to be smoothed to avoid interference.

When the device is turned on, no one touches it, so record the charging time as a benchmark.

If someone touches it, the charging time will be longer, so check the charging time regularly.

If you find that the charging time is much longer than the benchmark charging time (I used twice the benchmark time for comparison), you can assume that someone has touched it.

It has been completed and put into use, and its reliability and anti-interference capabilities can meet the requirements.

void mw(){//main working loop

unsigned int i;

static unsigned int cdsj=0,bzz; //Charging time, standard value

static unsigned char csh=10; //initialize count

T2H=T2L=0; //Counter 2 count value is initialized to 0

P3M1 |=0x8; //p3.3 is set to open drain state

P3M0 |= 0x8; //

P3_3=0; //p3.3 output cleared to 0

delay(100);

P3M1 |=0x8; //p3.3 is set to high impedance state

P3M0 &=0xf7;//

AUXR |= 0x10; //Start counter 2

P3_3=1; //p3.3 output is 1, input state

IE1=0; //Clear the status of external interrupt 1

EX1=1; //Open external interrupt 1

while(EX1); //External interrupt is not completed and waiting in loop

i=cdsj>>3;

cdsj=cdsj-i+T2L; //smoothing

if(csh){

csh--;

if(csh==0){//The initial 10 counts are completed, and the current value is taken as the standard value

bzz=i+i;

};

return;

};

if(i>bzz){

This condition is met to indicate that the switch is touched

};

}